European patent No. 0 360 730 describes a flexible semi-bulk container that is suitable for use with fluidized solids, semi-solids, slurries and liquids and for shipping in less than truckload shipments where the package should have adequate stability to stand alone.
In one embodiment the container has a flexible body portion formed with side walls, a top wall and a bottom wall, access spouts in the body portion to fill and empty the body portion with fluidizedmaterial, and rigid panels associated with at least two opposing ones of the body side walls for providing rigidity sufficient to impart adequate stability to the flexible body portion to enable it to stand alone when filled with a fluidized material. The container has double layer side walls, these side walls having a space therebetween and one of the rigid panels is fixedly inserted in the space in at least two of the opposing side walls.
In another embodiment the rigid panels form a four-sided sleeve.
U.S. Pat. No. 4,622,693 describes a packaging assembly wherein a protective liner is affixed to the interior surface of a flexible bag in a manner such that the packaging assembly folds flat for storage transport and is readily converted to a substantially rectangular box for folding. It is apparent from the description that the container disclosed is intended for food products such as ribs or loin and is not suitable for use with bulk fluidized materials as evidenced by the use of light-weight paperboard etc.
U.S. Pat. No. 3,896,991 describes a flexible semi-rigid fabricating material comprising a laminate of top and bottom layers of relatively thin synthetic plastic film and a middle-layer of semi-rigid sheet material. This arrangement can be folded into a dimensional container.
While the rigid panels within the double-side wall or the sleeve described in EP 0 360 730 are said to impart sufficient rigidity to the container to allow it to stand alone when filled with a fluidized material the container does not overcome a number of perceived disadvantages.
While the rigid panels or sleeves do aid the container to retain its square or rectangular shape more closely than a container without the rigid panels would otherwise do, the container still tends to bulge out of shape. Also the corners of the container tend to become more than the nominal angle e.g. 90.degree. in the case of a four-sided container. The container thus loses its definitive square or rectangular shape. Each such container may have an unique shape due to varying degrees of bulging. For transport purposes it is desirable that a container for fluidized material retains its square or rectangular shape in order to minimize space between containers when placed side by side in an array. This shape requirement is not fulfilled by the contents of the prior art. Furthermore it is also desirable that flexible bulk containers are stackable. At present it is extremely difficult if not impossible to arrange the containers of the prior art one on top of the other when filled with fluidized material. This is due to the nature of the contents of the container whose fluid motion causes both the container on top and that underneath to deform further when stacked. The lack of exactly matching cross-sectional shapes on the ends of the containers which abut, together with motion of the fluidized material during transport makes stacking of the containers very unstable and hazardous. In the event a container stacked as described above falls from its position it is likely to burst open spilling its contents.